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The Mycota or Fungi are non-photosynthetic eucaryotes adapted
to absorptive nutrition. Slime molds have motile, unicellular, vegetative
stages, while true fungi form branched filaments (hyphae) that invade dead
or decaying material. All fungi form spores; the various groups of fungi
are distinguished by their means of spore formation. General characteristics of fungi: Plastids and chlorophyll are absent. Cell walls are made of chitin, not cellulose. Cell membranes sometimes break down to form binucleated cells or multinucleated aggregates. Reproductive structures vary, but spores are always produced. Nutrition is usually absorptive; many fungi live on dead or decaying matter (saprophytic), but some are parasitic instead. Fungi are important as decay organisms in freshwater and terrestrial ecosystems. Most prefer moist conditions for optimal growth. Slime molds: Fungi whose unicellular vegetative stages are either amoeboid or flagellated and resemble Protozoa. All types have a multinucleated or multicellular creeping stage that forms spore-producing bodies. Each spore develops into a new vegetative cell. True fungi (Eumycota): Fungi whose vegetative structure typically consists of a series of branching filaments (hyphae) forming a tuft (mycelium). Fungi with aquatic stages: Four primitive classes of fungi still reproduce by flagellated cells (zoospores). Zygomycetes (black bread molds, etc.): Reproduce by conjugation of hyphae that come together and form nonmotile spores. Ascomycetes (yeasts, common bread molds, cup fungi, truffles, etc.): spores are produced, 4 or 8 at a time, in sacs (asci). Basidiomycetes (mushrooms, puffballs, rusts, smuts, etc.): spores are produced, usually 4 at a time, at the tips of club-like organs (basidia). Deuteromycetes ("fungi imperfecti"): Fungi with no known sexual stages. Lichens: Very intimate symbiotic associations of fungi with either algae or cyanobacteria. The fungus absorbs and retains sufficient moisture for both partners; the green partner photosynthesizes and provides food. Lichens are often the first colonizers of bare rock surfaces. |
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